|Abstract||The work in this dissertation deals with the continued development of new methodologies for P-C and P-O bond formation using alternative methods that avoid the use of PCl3. A review of the relevant literature that proceeds this work is presented in Chapter 1. Chapter 2 describes the study of the P(III) to P(V) tautomerization of phosphinylidene compounds and the structural influences that effect the thermodynamic and kinetic properties to favor the more reactive P(III) species. A collaboration using both computational and experimental methods, show that electron withdrawing groups such as phenyl stabilize the tautomerization of phosphinylidene compounds. The second part of this work highlights the influence of various catalysts on P(III) to P(V) tautomerization. Using computational chemistry as a screening tool, a variety of organic acids and bases were tested. The calculations and experimental results are in good agreement.^Chapter 3 describes the work to develop the nickel-catalzyed hydrophosphinylation of unactivated alkenes, an extension of the work started with the nickel-catalyzed hydrophosphosphinylation of alkynes. The results show that nickel chloride is pre-activated to an active Ni(0) species and can be stabilized by the inexpensive bisphosphine ligand, ethylbis(diphenylphosphine), dppe. The reaction occurs at room temperature and works on a variety of different alkene substrates. Other manipulations used in tandem with the initial nickel hydrophosphinylation are highlighted, and show the reaction to be a versatile tool for making alkyl-H-phosphinate derivatives as precursors for further use. Chapter 4 details the development of manganese-promoted intermolecular and intramolecular additions of alkenes, alkynes and aryl compounds with H-phosphinates is described.^The system utilizing catalytic Mn(OAc)2 either neat or in DMSO, is successful for a variety of different alkenes and two alkyne substrates. A more efficient and cost-effective system was recently developed for H-phosphinate arylations using catalytic Mn(OAc)2 and MnO2 as an oxidant, and further applied to alkene phosphonochlorination with LiCl. In Chapter 5, nickel-catalyzed oxidation of alkyl hypophosphites is utilized to prepare ubiquitous alkyl-H-phosphonates starting from hypophosphorous acid and avoiding the use of PCl3. The reaction can be considered a form of water splitting. The studies show that after the intitial esterification step, NiCl2 or Ni/SiO2 is enough to oxidize the first P-H bond to form the desired phosphonate. The reaction has been applied to the synthesis of the global herbicide glyphosate.